High voltage circuit-breakers exist comprising a sealed insulating enclosure having a set of fixed contacts and a set of moving contacts located therein, with each set of contacts including a main contact and an arcing contact.
The inside of the enclosure is filled with a dielectric gas which is at least partially constituted by sulfur hexafluoride at a pressure of several bars.
When the temperature of the circuit-brealer's environment falls, the temperature of the gas inside the circuit-breaker also falls, thereby reducing its pressure.
Such a reduction in pressure lowers the dielectric strength of the circuit-breaker and this may lead to arcs being re-struck between the contacts during circuit interruption.
An aim of the present invention is to provide a circuit-breaker which will continue to operate properly even when the surrounding temperature falls.